It is well known to use certain chemicals and mixtures of chemicals as fire retardants for materials such as fabrics, rigid and flexible plastics foamed and non-foamed, timber, particle board and the like. The kinds of fire retardant agents employed vary with the material of interest and thus fire retardant agents considered suitable for application to one type of material may be completely unsuitable for another.
In the polyurethane industry, inorganic fire retardants which are soluble in nature are generally disregarded because they will leach from the polyurethane foam with deleterious results. For example, it is known from the literature the difficulties encountered with the soluble nature of ammonium monophosphate.
U.S. Pat. No. 3,423,343 assigned to Monsanto Company also discloses the above problem with ammonium monophosphate and ammonium orthophosphates in general and discusses the additional problem encountered with loss of physical properties such as compressive strength and closed cell content.
The above patent proposes the use of phosphorus and nitrogen compounds in the form of substantially water insoluble ammonium polyphosphates, having P--O--P type linkages and the general formula: EQU H(r-m).sub.+2 (NH.sub.4).sub.m P.sub.n O.sub.3n+1
where n is an integer having an average value greater than 10 and m/n is between about 0.7 and about 1.1 and the maximum value of m is equal to n+2.
Now, this compound sold under the trade name PHOSCHEK 30 by Monsanto Company is certainly less soluble than ammonium monophosphate or ammonium diphosphate and is described by Lewin, Atlas & Pearce, Vol 1, "Polyurethane Structure and Flame Resistance" to have flame spread of 36% after 7 days immersion in water, as opposed to 33% before immersion. However, Miles, C. E and Lyons, J. W report in "Properties of Rigid Urethane Foams Containing Fire Retardants based on Phosphorus", Journal of Cellular Plastics, p 539, December 1967 that polyurethane rigid foams containing this ammonium polyphosphate require a chlorofluorinated compound (CFC) blowing agent, trichlorofluoromethane in manufacture, and demonstrated an average weight loss of 10.0% upon ignition.
Leaving aside the issue of the use of a CFC blowing agent, in itself undesirable, for the present further disadvantage may occur in that the decomposition temperature is such that a reduced amount of char is formed. This results in either reduced fire protection or the increased expense of using more material to achieve adequate protection.
Thus, present development in the art favours the use of organic fire retardants for use in polyurethane applications.
For example, U.S. Pat. No. 4,623,672, assigned to Bayer AG, discloses flame retardant isocyanate addition products made by reacting an isocyanate with a compound selected from the group consisting of 1-phosphonoethane-2-carboxylic acid-tri-C.sub.1 -C.sub.4 -alkyl esters, 1-phosphonopropane-2-carboxylic acid-tri-C.sub.1 -C.sub.4 -alkyl esters and mixtures thereof. Blowing agents may include CFC agents, the examples particularly specify the use of trichlorofluoromethane, and foams prepared in accordance with this patent are ignitable.
Australian Patent No. 591089 assigned to Ciba-Geigy Limited employs as fire retardant a salt formed by reaction between dimethyl methyl phosphonate, monomethyl methyl phosphonate and a compound of the general formula (I): ##STR1## in which X is O,S or NH, R.sup.1 is H, alkyl with 1 to 4 carbon atoms, alkenyl of up to 4 carbon atoms, CN, CONH.sub.2 or NH.sub.2, R.sup.2 is H, alkyl with 1 to 4 carbon atoms or alkenyl of up to 4 carbon atoms or R.sup.1 and R.sup.2 together with the nitrogen atom to which they are attached form a heterocyclic ring of up to 6 carbon atoms which may optionally contain another heteroatom and R is H, an alkyl group with 1 to 8 carbon atoms, an aryl group with 6 to 10 carbon atoms, a cycloalkyl group with 5 to 12 carbon atoms or a heterocyclic group with up to 9 ring carbon atoms or a heterocyclic group with up to 9 ring carbon atoms, or, together with R.sup.1 forms an alkylene chain of 3 to 10 carbon atoms, or R is a group NHR.sup.3 wherein R.sup.3 is H, alkyl with 1 to 4 carbon atoms, alkenyl of up to 4 carbon atoms, CN, CONH.sub.2 or NH.sub.2 or together with R.sup.1 forms an alkylene chain of 2 or 3 carbon atoms, or R is a group ##STR2## where R.sup.1, R.sup.2 and X are as defined above and R.sup.4 is a direct bond or an alkylene group having up to 8 carbon atoms or is an arylene group having 6 to 10 carbon atoms.
These flame retardants are of low volatility and allow the formation of polyol formulations which are stable on storage. Again CFC blowing agents, namely dichlorodifluoromethane or trichlorofluoromethane, are noted as being especially desirable and trichlorofluoromethane is exemplified. Tests conducted according to German Standard DIN 4102 B2 reported a burn time of 9 to 15 seconds with one of the examples burning with maximum flame height 13 cm but no burn time being recorded. In all cases, loss on ignition or oxygen index is greater than 23.5% by weight.
U.S. Pat. No. 4,895,878 assigned to Recticel discloses the use of a fire retardant comprising at least one of the components: (1) linear urea-formol oligomer mixture having the general formula NH.sub.2 --CO--NH--CH.sub.2 --NH--CO--NH!.sub.n --CH.sub.2 --NH--CO--NH.sub.2 wherein n is from 0 to 50: (2) urea in powdered form of which the particles are at least partially recovered by a less soluble film, being sulphur or a resin; (3) dicyandiamide having the general formula: ##STR3##
A secondary fire retardant, for example, tris-(2-chloroethyl)-phosphate may also be included in the formulation together with a mixture of trichlorofluoromethane and methylene chloride as the blowing agent, so again the use of a CFC blowing agent is proposed.
Foams prepared in accordance with U.S. Pat. No. 4,895,878 burn with loss on ignition of 23 to 34% by weight and when exposed to a blowtorch test with an oxygen rich flame with length 15 cm at 1100.degree. C. applied perpendicular on a 3 cm large test steel plate during 30 seconds at a distance of 3 cm (between the output of the blowtorch and the test steel) burn, at best, within 10 seconds.
The burning behaviour of polyurethane foams prepared in the accordance with the above may be satisfactory for some applications but there is a need to produce polyurethane foams with greater fire resistance, especially flexible foams which have generally lower fire retardance than rigid foams.
Further, the prior art suggests that CFC blowing agents are still very much a feature of the polyurethane manufacturing industry. However, this situation cannot continue. As a result of an International Agreement, the use of CFC agents must be phased out by the year 1997 due to the atmospheric damage apparently caused by such agents. This clearly poses a serious technical problem for the polyurethane industry since blowing agents are presently perceived as essential to the formation of commercial foams. Blowing agents are introduced to polyurethanes and other polymers during manufacture to cause gas evolution which allows the production of the cellular structure in foams commonly encountered in packaging, furniture and building products as well as other applications.
Two types of foam are employed--these being the flexible type and the rigid type. Both types of foam have a cellular structure and are made from the same basic ingredients. These ingredients are bought as a "system" from large chemical companies and are tailored to achieve individual specifications suitable for various applications. Accordingly, and as the described prior art illustrates, technical pressures exist on chemical companies to produce foams with the required properties.
It is the general object of the present invention to provide a fire retardant agent for plastic foams that is substantially free of the above described limitations.
It is a first specific object of the present invention to provide a fire retardant agent that has substantially reduced ignitability from prior art fire retardant agents as described above.
It is a second specific object of the present invention to provide a fire retardant agent, that through its nature, allows the use of CFC blowing agents to be avoided.
It is a third specific object of the present invention to provide a fire retardant agent, formulated from compounds which are of economically sustainable cost.
It is a fourth specific object of the present invention to provide a process for the manufacture of a plastic, especially polyurethane, foam which allows the attainment of good physical properties such as compressive strength and good fire retardance.